1. Field of the Invention
The present invention relates to a semiconductor integrated circuit including an electrostatic discharge (ESD) protection circuit.
2. Description of the Prior Art
In recent years, semiconductor integrated circuits have been becoming vulnerable to damage by electrostatic discharge (hereinafter, referred to as “surge”) due to advancement in high integration in parallel with improved device miniaturization and higher density. For example, there is a higher probability that surge which comes in via an external connection pad (external pad) destroys devices of an input circuit, output circuit, input/output circuit, internal circuit, or the like, thereby deteriorating the performance of the devices. Thus, the semiconductor integrated circuits have an electrostatic discharge (ESD) protection circuit between the external connection pad and the input circuit, output circuit, input/output circuit or internal circuit for protection from surge.
Further, a high-speed interface capable of a transfer rate on the order of several gigahertzs (GHz) has been demanded due to increased operation speed and increased number of functions in personal computers, routers, peripheral devices, etc. Therefore, for an input/output circuit used for such a high-speed interface, it is necessary to use an ESD protection circuit of a low-capacitance type which is less influential on the waveform of data to be transferred.
FIG. 4 shows the structure of a conventional ESD protection circuit. As shown in FIG. 4, the conventional ESD protection circuit includes a diode 103 which has the anode connected to an external pad 100 and the cathode connected to a power supply line 101, and a diode 104 which has the cathode connected to the external pad 100 and the anode connected to a ground line 102.
When surge of positive charge comes in via the external pad 100, a current flows from the external pad 100 to the power supply line 101 via the diode 103, so that the surge of positive charge is discharged to the power supply line 101. When surge of negative charge comes in via the external pad 100, a current flows from the ground line 102 to the external pad 100 via the diode 104, so that the surge of negative charge is discharged to the ground line 102.
In this way, the conventional ESD protection circuit protects a circuit which is to be protected.